1. Technical Field
The present invention relates to an electric field light emitting device of a direct current driving type in which nitride semiconductor phosphor particles having a wurtzite crystal structure are used.
2. Background Art
Among light emitting devices operated by a direct electric current, as practicable semiconductor materials to be used for light emitting devices, such as a blue light-emitting diode (Blue-LED) and an ultra-violet light emitting diode (UV-LED), in particular, GaN-based semiconductors typified by gallium nitride (GaN), indium nitride-gallium mixed crystal (InGaN), aluminum nitride-gallium mixed crystal (AlGaN) and indium nitride-aluminum-gallium mixed crystal (InAlGaN) have become a focus of attention, and researches and developments thereof have been vigorously carried out.
Conventionally, such a GaN-based semiconductor is manufactured as a single crystal thin film by allowing the semiconductor material to grow on a substrate by using an MOCVD (Metal Organic Chemical Vapor Deposition) method. However, it is very difficult to form a single crystal thin film with a large area of the GaN-based semiconductor by using the MOCVD method.
Meanwhile, as another candidate for the light emitting device to be operated by a direct electric current, an organic EL is proposed. The organic EL has an advantage in that it can be produced at low costs since it can be manufactured by using an inexpensive process such as vapor deposition and an inexpensive substrate such as a glass substrate can be used. However, the organic EL has a problem of reliability.
For this reason, a method has been proposed in which an inorganic phosphor is handled not as a thin film but as particles, so that by arranging the particles, a light emitting device is formed. The advantages of this method for the inorganic thin film dc light emitting device are that an inorganic phosphor can be generated on an inorganic thin film dc light emitting device without being influenced by the substrate or the like, and that a large-size screen can be easily formed by using this element. The advantages for the inorganic EL include the fact that, since an inorganic substance can be used as the phosphor, high reliability can be ensured. For example, a structural example has been proposed in which inorganic phosphor particles are arranged so that a light emitting device is formed as shown in Japanese Patent Laid-open Publication No. 2006-117735. This Japanese Patent Laid-open Publication No. 2006-117735 has proposed a technique in which, on the surface of a nitride semiconductor forming a nucleus, a light emitting layer made of another nitride semiconductor is present, and a nitride semiconductor layer is laminated on the light emitting layer so that these nitride semiconductor, light emitting layer and nitride semiconductor layer are allowed to form a quantum well structure.